Su. Chon et Cj. Nelson, Effects of experimental procedures and conditions on bioassay sensitivity of alfalfa autotoxicity, COMM SOIL S, 32(9-10), 2001, pp. 1607-1619
Sampling procedures of the donor material, conditions of the assay, and sel
ection of test organism influence the sensitivity of a bioassay. Autotoxici
ty affects success of alfalfa (Medicago sative L.) reseeded after old alfal
fa. Root length is a more sensitive parameter to autotoxin than germination
or hypocotyl length. Our specific objective was to improve the sensitivity
of an alfalfa seedling bioassay for a better understanding of the autotoxi
city mechanism. Using a petri-dish assay with imbibed seed, we found extrac
t of alfalfa leaves was more autotoxic than either that of stems or seed. E
xtracts from oven-dried samples were stronger than those from freeze-dried
samples. Sterilization through membrane filtering or autoclaving did not al
ter autotoxicity bioassay. Root length at 25 or 50 seed/plate was more sens
itive to the extracts than that at 100 or 200 seed/plate. Roots from older
seedlings were more tolerant to the extracts than did those from seed or yo
unger seedling and had more branch roots to escape the autotoxin(s). These
results suggest that extracts from leaf samples that oven-dried and sterili
zed by filtering or autoclaving can improve the consistency and precision o
f bioassay. The bioassay was suitable with 25 to 50 seed per petri dish to
minimize interaction on interference (e.g., competition and autotoxicity fr
om testing seed itself). The bioassay can be improved by using very young r
oots from imbibed seed which are more sensitive to the autotoxin.